Very likely, the obscuring torus has both a Compton thick parsec-scale
component and a larger 100 pc-scale component which is
coplanar with the galactic disk and characterized by lower NH
(which does not violates the mass constraints). The internal torus obscures
completely the BLR along the intercepting lines of sight (Sy2 case), while the
obscuration due to the external torus (in edge-on systems) is moderate and
the Seyfert nucleus might show weak broad lines and, therefore, might
be classified
as intermediate type 1.8-1.9. Indeed, intermediate type Sys are more
commonly found in edge-on galaxies
(Maiolino & Rieke 1995).
This model is
also supported by the distribution of absorbing column of intermediate
Seyferts, which is significantly shifted towards lower values of
NH than strict Sy2s
(Risaliti et al. 1999,
Fig. 1).
Although, this model might apply to many
intermediate type Seyferts, there are Seyfert galaxies
whose intermediate properties are not
to ascribe to moderate obscuration but to photoionization and
variability effects or to more complex forms of absorption
(Goodrich et al. 1995,
Komossa & Fink 1997).